Solid state lighting devices with low contact resistance and methods of manufacturing
Solid state lighting (“SSL”) devices with improved contacts and associated methods of manufacturing are disclosed herein. In one embodiment, an SSL device includes a first semiconductor material, a second semiconductor material spaced apart from the first semiconductor material, and an active region between the first and second semiconductor materials. The SSL device also includes a contact on one of the first or second semiconductor materials. The contact includes a first conductive material and a plurality of contact elements in contact with one of the first or second conductive materials. The contact elements individually include a portion of a second conductive material that is different from the first conductive material.
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This application is a continuation of U.S. application Ser. No. 12/872,137 filed Aug. 31, 2010, now U.S. Pat. No. 8,536,595, which is incorporated herein by reference in its entirety.
TECHNICAL FIELDThe present disclosure is related to solid state lighting (“SSL”) devices with low contact resistance and associated methods of manufacturing.
BACKGROUNDMobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., LEDs) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination.
As discussed in more detail below, it has been observed that materials with good transparent or reflective properties often do not form satisfactory Ohmic contacts with components of the SSL structure 11, and vice versa. For example, the SSL device 10 having ITO in contact with the P-type GaN 18 may have undesirable high series resistance. In another example, silver processed to maintain its reflectivity may form a Schottky barrier with the P-type GaN 18. The high series resistance and/or Schottky barrier may result in parasitic electrical impedance during operation and/or otherwise degrade the electrical performance of the LED devices. In yet another example, if silver is annealed at high temperatures to form good electrical contact with the SSL structure 11, its reflectivity may degrade. Accordingly, it would be desirable to mitigate the impact of electrical contact resistance in SSL devices.
Various embodiments of SSL devices with low contact resistance and associated methods of manufacturing are described below. As used hereinafter, the term “SSL device” generally refers to devices with LEDs, organic light emitting diodes (“OLEDs”), laser diodes (“LDs”), polymer light emitting diodes (“PLEDs”), and/or other suitable sources of radiation other than electrical filaments, a plasma, or a gas. A person skilled in the relevant art will also understand that the technology may have additional embodiments, and that the technology may be practiced without several of the details of the embodiments described below with reference to
In certain embodiments, the substrate material 102 can include silicon (Si), at least a portion of which has the Si(1,1,1) crystal orientation. In other embodiments, the substrate material 102 can include silicon with other crystal orientations (e.g., Si(1,0,0)), AlGaN, GaN, silicon carbide (SiC), sapphire (Al2O3), zinc oxide (ZnO2), a combination of the foregoing materials and/or other suitable substrate materials. In the illustrated embodiment, the substrate material 102 has a generally planar surface 111 proximate to the optional buffer material 103. In other embodiments, the substrate material 102 may also include a non-planar surface (e.g., having openings, channels, and/or other surface features, not shown).
The optional buffer material 103 can facilitate the formation of the first and second semiconductor materials 104 and 108 and the active region 106 on the substrate material 102. In certain embodiments, the optional buffer material 103 can include at least one of aluminum nitride (AlN), aluminum-gallium nitride (AlGaN), zinc nitride (ZnN), GaN, and/or other suitable materials. In other embodiments, the optional buffer material 103 may be omitted, and the first semiconductor material 104 may be formed directly on the substrate material 102.
In certain embodiments, the first semiconductor material 104 can include N-type GaN (e.g., doped with silicon (Si)), and the second semiconductor material 108 can include P-type GaN (e.g., doped with magnesium (Mg)). In other embodiments, the first semiconductor material 104 can include P-type GaN, and the second semiconductor material 108 can include N-type GaN. In further embodiments, the first and second semiconductor materials 104 and 108 can each include at least one of gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), gallium(III) phosphide (GaP), zinc selenide (ZnSe), boron nitride (BN), AlGaN, and/or other suitable semiconductor materials.
The active region 106 can include a single quantum well (“SQW”), MQWs, and/or a bulk semiconductor material. As used hereinafter, a “bulk semiconductor material” generally refers to a single grain semiconductor material (e.g., InGaN) with a thickness greater than about 10 nanometers and up to about 500 nanometers. In certain embodiments, the active region 106 can include an InGaN SQW, GaN/InGaN MQWs, and/or an InGaN bulk material. In other embodiments, the active region 106 can include aluminum gallium indium phosphide (AlGaInP), aluminum gallium indium nitride (AlGaInN), and/or other suitable materials or configurations.
In certain embodiments, the first semiconductor material 104, the active region 106, the second semiconductor material 108, and the optional buffer material 103 can be formed on the substrate material 102 via metal organic chemical vapor deposition (“MOCVD”), molecular beam epitaxy (“MBE”), liquid phase epitaxy (“LPE”), and/or hydride vapor phase epitaxy (“HVPE”). In other embodiments, at least one of the foregoing components may be formed via other suitable epitaxial growth techniques.
In certain embodiments, the first contact 120 can include copper (Cu), aluminum (Al), silver (Ag), gold (Au), platinum (Pt), and/or other suitable conductive material. In other embodiments, the first contact 120 can include ITO, aluminum zinc oxide (“AZO”), fluorine-doped tin oxide (“FTO”), and/or other suitable transparent and conductive oxide (“TCOs”). Techniques for forming the first contact 120 can include MOCVD, MBE, spray pyrolysis, pulsed laser deposition, sputtering, electroplating, and/or other suitable deposition techniques.
The second contact 122 can include a conductive material 123 and a contact material 118 between the second semiconductor material 108 and the conductive material 123. The conductive material 123, for example, can be a transparent conductive material. As shown in
The contact material 118 can include a material that forms satisfactory mechanical and/or electrical contact with both the second semiconductor material 108 and the conductive material 123. In certain embodiments, the conductive material 123 includes ITO, AZO, FTO, and/or other suitable TCOs. The contact material 118 can include silver (Ag). Without being bound by theory, it is believed that silver can form good electrical contact with both the second semiconductor material 108 and the conductive material 123 containing a TCO without high series resistance or forming a Schottky barrier. Thus, the interface between the contact material 118 and the second semiconductor material 108 has a higher electrical conductance than the interface between the conductive material 123 and the second semiconductor material 108. As a result, compared to the contact described above in the Background section, the electrical connection between the second semiconductor material 108 and the conductive material 123 can be improved by interposing the contact material 118 therebetween. In other embodiments, the contact material 118 can also include gold (Au), platinum (Pt), and/or other suitable metals.
In the illustrated embodiment, the contact material 118 extends from the surface 108a of the second semiconductor material 108 to an intermediate depth d between the first and second surfaces 123a and 123b. In other embodiments, at least a portion of the contact material 118 may extend the entire depth D between the first and second surfaces 123a and 123b. In further embodiments, the SSL device 100 may include a support material (not shown) that holds the contact material 118, as discussed in more detail below with reference to
The contact material 118 can also have a pattern and/or other characteristics such that the contact material 118 does not significantly affect the optical property of the conductive material 123. For example, the optical property of the combined conductive material 123 and the contact material 118 can be generally similar to that of the conductive material 123 by itself. As shown in
At least one of a spacing P, size, shape, and quantity of the contact elements 125 may be adjusted to determine the pattern and/or other characteristics. In certain embodiments, the spacing P, size, shape, and quantity of the contact elements 125 may be adjusted based on empirical data. In other embodiments, the spacing P, size, shape, and quantity of the contact elements 125 may be adjusted based on light interference calculations. In further embodiments, a combination of the foregoing techniques may be used.
Even though the contact elements 125 are shown as having generally the same shape and size in
In further embodiments, the conductive material 123 and the contact material 118 may include a generally similar material (e.g., silver) but formed with different processes. For example, in one embodiment, the contact material 118 containing silver may be formed initially on the surface 108a of the second semiconductor material 108. The formed contact material 118 may be annealed to yield a satisfactory electrical connection with the second semiconductor material 108. However, it is believed that the annealing process may degrade the reflectivity of the contact material 118. To at least reduce the impact of the reflectivity reduction, the conductive material 123 also containing silver may be formed on the second semiconductor material 108 and the contact material 118 without undergoing annealing. Thus, the conductive material 123 may still retain its good reflectivity. As a result, in the foregoing embodiment, the second contact 122 is substantially entirely constructed from silver but is still patterned to yield a good balance between reflectivity and contact resistance.
In further embodiments, the contact material 118 and/or the conductive material 123 may be formed via other suitable techniques. For example, instead of forming the contact material 118 through the apertures 132 in the masking material 130, the contact material 118 may be formed to cover a substantial portion of the surface 108a of the second semiconductor material 108. The formed contact material 118 may then be patterned and etched to form the array shown in
Even though the SSL device 100 is shown in
In certain embodiments, the support material 114 can include a TCO that is different from the conductive material 123. For example, the support material 114 can include AZO while the conductive material 123 includes ITO. In other embodiments, the support material 114 can also include a TCO that is generally similar to that of the conductive material 123. In further embodiments, the support material 114 can include silicon dioxide (SiO2), silicon nitride (SiN), and/or other dielectric and transparent materials.
Referring back to
Without being bound by theory, it is believed that aluminum is highly reflective. As a result, more light may be extracted from the first semiconductor material 104 when aluminum is used as the conductive material 123 in the second contact 122. However, it is also believed that aluminum forms a Schottky barrier with GaN, InGaN, or other types of semiconductor materials. As a result, the second contact 122 may have poor electrical properties (e.g., high forward-voltage drop). It is further believed that silver can form generally Ohmic contacts with both aluminum and GaN, InGaN, or other types of semiconductor materials. Accordingly, by interposing the contact material 118 containing silver between the conductive material 123 and the second semiconductor material 108, electrical connections can be improved over conventional devices while the reflective property of the conductive material 123 is maintained.
Even though the SSL device 200 is shown in
From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the disclosure is not limited except as by the appended claims.
Claims
1. A solid state lighting (SSL) device, comprising:
- a first semiconductor material;
- a second semiconductor material spaced apart from the first semiconductor material;
- an active region between the first and second semiconductor materials; and
- a contact on one of the first and second semiconductor materials, the contact including a first material that is transparent and conductive, a second material that includes silver in contact with both the first material and the one of the first and second semiconductor materials, and a support material between the first material and the first semiconductor material,
- wherein the support material is transparent and conductive, the support material has a first support surface in contact with the first semiconductor material and a second support surface in contact with the first material, the support material has a plurality of apertures extending between the first and second support surfaces, the apertures individually contain a portion of the second material, and the second material forms an Ohmic contact with the first material, the support material, and the one of the first and second semiconductor materials.
2. The SSL device of claim 1 wherein the first material includes at least one of indium tin oxide, aluminum zinc oxide, and fluorine-doped tin oxide.
3. The SSL device of claim 2 wherein the support material includes at least one of indium tin oxide, aluminum zinc oxide, and fluorine-doped tin oxide.
4. The SSL device of claim 1 wherein the second material includes a plurality of pillars arranged in an array.
5. The SSL device of claim 1 wherein the second material includes a plurality of contact elements arranged in an array with a spacing between individual contact elements that is at least three times of a size of the individual contact elements.
6. The SSL device of claim 1 wherein:
- the contact is a first contact on the first semiconductor material;
- the SSL device further includes a second contact on the second semiconductor material;
- the second contact is spaced apart from the first contact by the first semiconductor material, the active region, and the second semiconductor material;
- the first semiconductor material includes a P-type gallium nitride (GaN) material;
- the second semiconductor material includes an N-type GaN material; and
- the active region include at least one of a bulk indium gallium nitride (InGaN) material, an InGaN single quantum well (“SQW”), and GaN/InGaN multiple quantum wells (“MQWs”).
7. A method of forming a solid state lighting (SSL) device, comprising:
- forming an SSL structure on a substrate material, the SSL structure including a first semiconductor material, a second semiconductor material spaced apart from the first semiconductor material, and an active region between the first and second semiconductor materials;
- forming a plurality of contact elements on one of the first and second semiconductor materials, wherein forming the plurality of contact elements includes depositing a support material onto the one of the first and second semiconductor materials, wherein the support material is transparent and conductive, patterning the support material to form a plurality of openings, and depositing silver onto the one of the first and second semiconductor materials via the openings, wherein the deposited silver forms a first Ohmic contact with the one of the first and second semiconductor materials; and
- depositing a conductive material onto the deposited silver and the support material, the conductive material being transparent and forming a second Ohmic contact with the deposited silver.
8. The method of claim 7 wherein the conductive material includes at least one of indium tin oxide, aluminum zinc oxide, and fluorine-doped tin oxide.
9. The method of claim 8 wherein the support material includes at least one of indium tin oxide, aluminum zinc oxide, and fluorine-doped tin oxide.
10. The method of claim 7 wherein forming the plurality of contact elements further includes pattering the support material to separate the openings by a predetermined amount of spacing between the individual openings.
11. The method of claim 7 wherein depositing the silver onto the one of the first and second semiconductor materials comprises forming a plurality of conductive pillars.
12. The method of claim 7 wherein depositing the silver onto the one of the first and second semiconductor materials comprises forming a plurality of conductive pads arranged in a uniform array.
13. The SSL device of claim 1 wherein the first conductive material is different than the support material.
14. The method of claim 7 wherein the conductive material is different than the support material.
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Type: Grant
Filed: Sep 17, 2013
Date of Patent: Jun 16, 2015
Patent Publication Number: 20140014999
Assignee: Micron Technology, Inc. (Boise, ID)
Inventor: Martin F. Schubert (Boise, ID)
Primary Examiner: Joseph Schoenholtz
Application Number: 14/028,784
International Classification: H01L 33/38 (20100101); H01L 33/40 (20100101); H01L 33/42 (20100101); H01L 21/02 (20060101);